TD-LTE goes mainstream with a new performance promise

IDG News Service - A version of LTE that could give consumers more mobile bandwidth for downloading content or apps is moving from the margins to the mainstream at Mobile World Congress this week.

TD (Time-Division) LTE, which uses a single block of radio frequencies instead of the paired blocks used in typical FDD (Frequency-Division Duplexing) cellular networks, has shown up in many places at the world's annual mobile gathering. Numerous carriers and vendors are building the technology into their gear and demonstrating uses for it, in a departure from the scant attention given TD-LTE a few years ago.

The big prize that shines over all this activity is the prospect of China Mobile's planned national deployment of TD-LTE, which is still waiting on the Chinese government's spectrum allocation but is already gathering steam with trial services in six cities. Yet carriers elsewhere are also using or planning to use TD-LTE, including Softbank in Japan, Sprint Nextel and Clearwire in the U.S., and operators in Brazil, Russia, India, Sweden, Saudi Arabia, and other countries. TD spectrum blocks are being set aside in yet other countries, including in a recent auction in the U.K.

"There's a lot of momentum behind it, and it's not all China," said Ovum analyst Daryl Schoolar. Still, with more than 600 million subscribers, China Mobile is big enough to make TD-LTE attractive to network vendors, chip designers and device makers for a long time, he said. "The volume opportunity is going to keep everyone interested."

At its booth at MWC, China Mobile showed off dozens of chips and devices designed for its planned network. They included smartphones from LG Electronics, Samsung Electronics, Huawei Technologies, ZTE and Quanta; USB dongles and personal hotspots from most of those vendors, and tablets from Huawei and Quanta. The display of chips included ones from big names such as Marvell Technology Group and Qualcomm. All those devices can be used with FDD as well as TD, along with backward compatibility with 2G and 3G networks.

Alcatel-Lucent has already developed a TD-LTE small cell, through subsidiary Alcatel Shanghai Bell, that will be used to add capacity to China Mobile's network in busy areas. Mindspeed Technologies, which supplied the silicon for it, showed off the cell at MWC.

Also at the show, Nokia Siemens Networks demonstrated a patented algorithm for balancing subscriber loads among LTE cells, including between TD and FDD equipment.

Advocates of TD-LTE say flexibility is its main advantage. Most LTE networks so far have been built with FDD (Frequency-Division Duplexing) technology, which uses two separate and equal-sized spectrum blocks, one for upstream and one for downstream traffic. Because TD-LTE uses just one large block, the frequencies within that block can be divided up in any way that makes sense for the way subscribers will use it.